The most common example of the need to monitor and act on the separation distances between one structure and another structure, is when one ship is being approached by another ship and then performing station keeping with that ship in order to transfer supplies between the two ships while at sea. This is referred to by the Navy as an UNREP or underway replenishment.
The current state of the art is for the two ships to approach each other using only a “feel” for the distance between the two ships. One it is thought that the two ships are close enough, a line is passed between them. The ships then back off from each other to the desired station keeping distance. The line has flags on it at regular intervals. Station keeping is performed by noting the number of flags hanging on the line between the two ships as the way of monitoring the separation distance between the two ships. This time-tested method is still the primary station keeping separation distance measuring tool in use today. It requires at least one person to manually haul on the flag rope and injuries have occurred. In addition the separation distance can only be estimated while approaching close enough to pass the flag line between the ships. The potential hazards of approaching too close to avoid contact is real. This invention will inform all parties involved of the current distance between the two ships both during the critical approach and the long station keeping phases to ensure that a safe distance is maintained between the two vessels at all times.